Cellulose is a linear polysaccharide of glucose residues connected by β-1,4 linkages. In nature, cellulose is usually associated with lignin together with hemicelluloses, such as xylans and glucomannans. Cellulolytic enzymes hydrolyze cellulose and are produced by a wide variety of bacteria and fungi. Cellulases are industrially important enzymes with a current annual market value of about 190 million US $. In the textile industry, cellulases are used in denim finishing to create a fashionable stone washed appearance in denim cloths in a biostoning process, and they are also used, for instance, to clean fuzz and prevent formation of pills on the surface of cotton garments. In detergent industry cellulases are used to brighten colors and to prevent graying and pilling of garments. Cellulases are further used in food industry and animal feed manufacturing, and they have a great potential in the pulp and paper industry, for instance, in deinking to release ink from fiber surfaces and in improving pulp drainage. The wide spectrum of industrial uses for cellulases has established a need for commercial cellulase products containing different cellulase components and functioning optimally in different pH and temperature ranges.
The practical use of cellulases is hampered by the nature of the known cellulases, which are often mixtures of cellulases having a variety of activities and substrate specificities. For this reason, efforts have been made to obtain cellulases having only the desired activities. The unique properties of each cellulase make some more suitable for certain purposes than others. While the enzymes differ in a number of ways, one of the most important differences is the pH optimum. Neutral cellulases are most active in the pH range 6-8 and alkaline cellulases in the pH range 7.5-10, whereas acid cellulases, having the pH optimum at pH 4.5-5.5, show very low activity levels at higher pH values. Neutral and acid cellulases are especially useful in the textile industry. In fabric treatment cellulases attack the chains of cellulose molecules that form the cotton fibers, thereby affecting the characteristics of the fabric.
In textile industry “stone washed” look or an abraded look has been denim producers' interest in recent years. Traditional stone washing with pumice stones reduces the strength of fabric and burdens the laundering apparatuses. The trend has been towards enzymatic denim finishing processes and cellulases have replaced or are being used together with pumice stones to give the fabric its desired “worn” look. Controlled enzyme treatment results in less damage to the garments and machines and eliminates the need for disposal of stones.
Cellulases applied in denim treatment are usually divided into two main groups: acid and neutral cellulases. Acid cellulases typically operate at pH 4.5-5.5 and the neutral cellulases in the range of pH 6-8. Acid cellulases used in biostoning mainly originate from Trichoderma reesei (sexual form Hypocrea jecorina) and the neutral cellulases come from a variety of fungi, including genera of Melanocarpus, Humicola, Thielavia, Myceliophthora, Fusarium, Acremonium, and Chrysosporium (Haakana et al. 2004). T. reesei enzymes include, e.g., cellulases from the glycoside family 5 (endoglucanase II, EGII), family 7 (cellobiohydrolase I, CBHI) and family 12 (endoglucanase III, EGIII; Ward et al. 1993), and the neutral cellulases, most often endoglucanases, from family 45 and family 7 (Henrissat, 1991; Henrissat and Bairoch, 1993).
Cellulases comprise a catalytic domain/core (CD) expressing cellulase activity. In addition to the catalytic domain the cellulase molecule may comprise one or more cellulose binding domains (CBDs), also named as carbohydrate binding domains/modules (CBD/CBM), which can be located either at the N- or C-terminus of the catalytic domain. CBDs have carbohydrate-binding activity and they mediate the binding of the cellulase to crystalline cellulose but have little or no effect on cellulase hydrolytic activity of the enzyme on soluble substrates. These two domains are typically connected via a flexible and highly glycosylated linker region.
Cellulases that attack primarily on the surface of the fiber are especially useful in stone washing of denim dyed with Indigo dye, as the dye is located on the surface of the fiber. When used to treat cotton fabric, neutral cellulases generally require a longer washing time than the acid cellulases. However, neutral cellulases have less aggressive action on cotton than acid cellulases, and do not affect on the strength of the fabric as much as acid cellulases. Neutral cellulases have a broader pH profile and thus the pH increase that occurs during biostoning has little effect on the activity of neutral cellulase enzymes. However, since cellulase treatments also have undesirable effects, such as fiber damage and strength loss, a suitable balance between the desired and unwanted effects has to be sought.
WO97/14804, which is incorporated herein by reference, discloses three novel neutral cellulases of Melanocarpus origin, which are especially useful in the textile and detergent industry. Specifically a 20 kDa endoglucanase (Cel45A), a 50 kDa endoglucanase (Cel7A), and a 50 kDa cellobiohydrolase (Cel7B) are described. These cellulases designated herein as “20K-cellulase”, “50K-cellulase”, and “50K cellulase B”, respectively, are derived from Melanocarpus albomyces and show good stone washing effects.
Since there is an existing demand, especially in the textile and detergent industry, for further improved cellulases, it has been suggested that improvements in cellulases could be obtained by forming fusion proteins. Also in WO97/14804 fusion protein constructs of 20K-cellulase, 50K-cellulase, and 50K cellulase B with, for instance, Trichoderma reesei cellulase, hemicellulase or mannase or functional domains thereof, are generally suggested. Further, in order to create new properties for the disclosed cellulases, fusions of the disclosed cellulases with domains, such as cellulose binding domain (CBD), preferably with its linker, are suggested. However, no specific examples are given, nor are described the new properties aimed to.
Cellulase fusion proteins are additionally known, for instance, from WO96/29397, which discloses endoglucanases formed by a fusion between endoglucanases from Myceliophthora thermophila, from Macrophomina phaseolina and from Crinipellis scabella and the CBD/linker from Humicola insolens. Said endoglucanases in their natural form do not have a CBD/linker.
EP 663 950 discloses cellulase variants, especially Humicola insolens 43 kDa cellulase variants, wherein the cellulase may include a linking region from another microorganism species, for instance for providing improved properties, such as improved resistance to anionic surfactants, to oxidation or to bleaching agents.
However, there is a continuous need for improved cellulases that also are less harmful to the fiber in textile industry and in other fields, where cellulases traditionally are used. In particular, there is a continuous need for more efficient cellulases to improve the process economics.
The present invention aims to meet this need.